This invention relates to injection molding and more particularly to an improved injection molding valve gated system for making a product with an opening extending through it.
This type of gating in which the valve pin extends completely through the cavity is known as core ring gating. The opening through the product is the hole formed by the valve pin. A system for core ring gating is described in Japanese patent application No. 55061438. However, the system shown in Japanese patent application No. 55061438 does not provide for sufficient cooling of the valve pin or for thermal separation between the hot nozzle and the cooled movable mold platen, and the present invention is an improvement over that system.
In a core ring gated injection molding system, the head portion adjacent the tip or forward end of the valve pin which extends through the cavity is received in the cooled movable mold platen on the other side. However, when the cavity has filled and the valve pin is actuated to the closed position, if the valve pin has a large diameter, an excessive amount of heat flows along it to the melt in the cavity and to the movable mold platen on the other side. In other words, it is difficult to cool the head portion of the valve pin with the result that the system will not operate quickly enough and there may be unsatisfactory shrinkage of the molded product. While the extent of this problem depends to some degree upon the type of material being molded and the shape of the product, generally speaking, the larger the diameter of the valve pin, the greater the problem.